Eviation Alice prototype fire

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cluttonfred

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I understand the drag benefits of placing the engine nacelles where then can counter the wingtip vortices, but yikes, what happens if one of those wingtip engines gives out during takeoff or initial climb?
 

Jay Kempf

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They have some sort of balancing system and emergency cutoff for the tip rotors. Not sure the drag benefit thing has ever been proven in real life. If they had gotten farther they would have actually proven or disproven.
 

bmcj

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I understand the drag benefits of placing the engine nacelles where then can counter the wingtip vortices
That was done in the Vought V-173 as well (I believe for the same reason), but I’m not sure if there was ever any quantitative measure to determine the benefit.
 

Wanttaja

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I understand the drag benefits of placing the engine nacelles where then can counter the wingtip vortices, but yikes, what happens if one of those wingtip engines gives out during takeoff or initial climb?
They have some sort of balancing system and emergency cutoff for the tip rotors.
Which means that an "engine failure" in a nominally twin-engine aircraft causes more than a 50% power loss. Single-engine go-arounds should be fun, too. Massive amount of yaw produced. Probably can program the computer so power comes in gradually, but that just means the power isn't there when the pilot asks for it.

Back in my control-line days, I built an airplane configured like this...two Cox .049 engines on the wingtips. Really acted weird when the outboard engine quit. If I tried to climb too fast, it would start rocking left and right. Classic VMC behavior, limited by the control lines. Losing the inboard engine made it start spiraling in at me....

The other factor that occurs to me, looking at that configuration, is crosswind landings. How close are those props going to get to the ground, with the usual wing-low compensation? How much will those wings rock, in gusts?

Ron Wanttaja
 

Victor Bravo

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I understand the drag benefits of placing the engine nacelles where then can counter the wingtip vortices, but yikes, what happens if one of those wingtip engines gives out during takeoff or initial climb?
I'm guessing that the reason for the engine in the tail is for just that. In the event of a wing engine failure, the power to the other wing engine is (automatically) reduced to 25-33% power, and the center engine goes to 110 or 115% emergency power, and you wind up with about the same amount of asymmetric thrust as if you were in a Baron or Twin Comanche. When you limp it around the pattern and land (immediately, not later at your destination), the center engine has been over-sped and over-temped and it has to be replaced.

The funny part to me is that with nothing more than the recent "Prantdl wing" concept being promoted by Al Bowers (small increase in span, increased twist to move the "vortex" inboard from the wingtip), they could probably realize almost as much real-world drag and efficiency improvement as the theoretical and highly problematic improvement from putting the propellers out at the tip.
 

cluttonfred

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This seems like a perfect case for a trimotor with different size engines, say 600 hp in the center engine and 300 hp each in the outboard engines, all normally operated at 2/3 power so you have 800 hp for take off. Lose a wingtip engine and you kill them both and up the center engine to 600 hp. Lose the center engine and you up the wingtip ones to 600 hp total. Economy cruise is 400 hp from the outboard engines only with the center engine prop folded or feathered. I have no idea of the actual power of this aircraft, but you get the idea.
 

Dan Thomas

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The other factor that occurs to me, looking at that configuration, is crosswind landings. How close are those props going to get to the ground, with the usual wing-low compensation? How much will those wings rock, in gusts?
That was one of my comments in the original thread on this thing. Crosswind landings will take the upwind prop out. You don't land a taildragger in a crab like airliners do now with their big turbofans so close to the ground.

The other problem I saw was that rear prop, its tips right close to the surface and the tailwheel just ahead of it. That predicts plenty of FOD damage to that prop.
 

Jay Kempf

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Having an unshrowded prop at a wingtip needs to be tested. The wings on this thing sag under the weight of the tip nacelles. Not hard to ground a prop in any sort of normal landing scenario in turbulent conditions and crosswind. I was also surprised this thing was a tail dragger. Not sure how insurance companies react to them anymore at that scale who knows. They are farther along than many other electric airplane companies.
 

12notes

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Which means that an "engine failure" in a nominally twin-engine aircraft causes more than a 50% power loss. Single-engine go-arounds should be fun, too. Massive amount of yaw produced. Probably can program the computer so power comes in gradually, but that just means the power isn't there when the pilot asks for it.

Back in my control-line days, I built an airplane configured like this...two Cox .049 engines on the wingtips. Really acted weird when the outboard engine quit. If I tried to climb too fast, it would start rocking left and right. Classic VMC behavior, limited by the control lines. Losing the inboard engine made it start spiraling in at me....

The other factor that occurs to me, looking at that configuration, is crosswind landings. How close are those props going to get to the ground, with the usual wing-low compensation? How much will those wings rock, in gusts?

Ron Wanttaja
It's a 3 engine aircraft, and if one of the outboard props stops, the other automatically does as well. The rear engine has enough power to climb on its own. This is from an article I linked to in the other thread when the exact same psychic engineering happened.

There are options with electric that you don't have with a piston engine. Stopping/starting a prop is trivial on electric as opposed to a probable emergency in a piston. You can stop the wing prop in a position with maximum ground clearance when close to the ground, and do so very rapidly, probably within 1 rotation. It can also go from stopped to full thrust very quickly (probably <1s), as the motor produces 100% torque at 0 RPM. I say probably, because there has been very little detailed information released, and there are a lot of variables in motor power and propeller size and weight, but they are reasonable assumptions.

It's probably much better to act as if at least one of these people involved in designing it has actual knowledge of flight dynamics than continue on as if the very thought of a crosswind or even landing at all never entered their mind. They have one prototype, with 2 more scheduled to be delivered this year. This is not some random yokel's sketch of what looked good, there has been a lot of engineering going into this design. The assumption that no one producing this plane has thought of something you deal with in your first few training flights is fairly silly.

There have been no damage reports, so I'm not sure why the OP says "major fire", neither the article linked nor the video says any such thing. All videos of the "fire" show firefighters just dumping water on the plane, no flames or smoke is visible, which is normal for firefighting (why use 100 gallons when 1000 will do?) Another article stated:
"The company said that the fire is believed to have been caused by a fault with a ground-based battery system. It has yet to confirm how extensively the prototype aircraft might have been damaged in the incident. The Prescott Fire Department was on standby for the planned test and quickly extinguished the fire, which caused no injuries."
https://www.ainonline.com/aviation-news/business-aviation/2020-01-24/eviations-electric-alice-aircraft-catches-fire-during-ground-tests

They designed and built a plane. It caught on fire on the ground, this is a sad thing.
 

12notes

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Nothing to see here. No reason to think twice about a fire on a highly (aerodynamically) speculative prototype aircraft with an uncertain financial future. It could happen to any airplane . . .
They have two more prototypes in production, and had the fire department on hand before they started the test. These are not the actions of anyone attempting fraud. There is no visible to damage to the plane in the pictures or video. No damage reports have been given. The CEO is a physicist who worked developing electric motors for vehicles before this, and the CTO is an aerodynamicist from Israel Aerospace. It is not a half-assed operation run by MBAs. They have $200 million in funding. Basically, 100% of your post is based on complete fiction.

And we're back to wild speculation based on almost zero facts with easily refuted assumptions thrown in being the way this board looks at any new aircraft. It's just sad. I'm not sure why anyone would willingly post about any new design here.
 

Dan Thomas

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And we're back to wild speculation based on almost zero facts with easily refuted assumptions thrown in being the way this board looks at any new aircraft. It's just sad. I'm not sure why anyone would willingly post about any new design here.
What is your aviation experience?
 

lr27

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I'm sure there's significant research on tip mounted props. I suspect that the flight testing and wind tunnel models of the V-173 revealed some useful info. There was also research on tip mounted turbines to recover a little energy from the vortices. And CFD, I gather, is far more capable then it used to be.
OTOH, stopping five bladed props shown at the Paris air show at any particular point won't help ground clearance much. That was a static model. Maybe the industrial designers and marketers haven't been speaking with the engineers. Some. Images of the Alice show two bladed props at the tips.

I wonder about takeoff with the prop so low in the back. Will there be some automatic gadget to keep the prop from getting too low? Maybe flaps will help. Maybe the rear prop is only used after the tail comes up?

Wikipedia says that batteries make up 60 percent of the takeoff weight. Doesn't leave a lot for the passengers, airframe, etc. Apparently they have also contemplated an aluminum-air battery, which is supposed to have much more energy per kg.
I'll be impressed if they pull this off, but I have to admit it reminds me of certain projects I used to see in Popular Mechanics.
 

lr27

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With the energy density of present day batteries, conventional airframe weights and propulsive efficiencies won't be very useful. Needing to do something doesn't make it easier, though.
I would like to see the Alice succeed, but I wonder how much the project owes to superior marketing as opposed to superior engineering. Seems like, to succeed in business, the former is essential but the latter isn't always necessary. Anyone else remember Pet Rocks?
 

bmcj

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Just spitting into the wind here, but isn’t it likely that the tail motor is lighter duty in order to avoid weighty motors and batteries (or heavy cables) behind the CG? They can carry the bulk of the battery weight in the wings where it would be closer to the tip motors and not impose a penalty in terms of long cables, CG arm or bending moment at the wing root.
 
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